What will happen to tropical forests with global warming is one of the largest uncertainties in the global carbon budget. As a start to address this important question, the International Institute for Tropical Forestry has initiated a warming experiment on understory vegetation in Puerto Rico. Hexagonal arrays of infrared heaters have been deployed around the periphery of 4-m-diameter plots at a height of 1.6 m above the vegetation. The vegetation is being warmed by 4 degrees C above the canopy temperature of control plots, as sensed by infrared thermometers. This degree of warming has not been sustained previously over plots as large as these. Therefore, the equipment chosen is larger than used before, and it has not been used for this application before. The experiment started on 28 September 2016.
Thermal images and photographs illustrate that the uniformity of the warming of the vegetation is good, especially considering the non-uniformity of the forest understory vegetation. The system has been able to maintain the 4 degree C rise in temperature very well except during periods of rain. Soil temperatures are also warming following the canopy above but with a lag. We conclude that the infrared heater system is indeed able to maintain the temperature rise of the plots as desired.